Doctors say the girl, now 2, has only trace amounts of HIV in her bloodstream and has been able to keep the virus in check without medication. The next step is to try to replicate the results.

For the first time, doctors are reporting that a child born with HIV and put on an unusually aggressive treatment regimen has been functionally cured of the infection.

Now 2 years old, the Mississippi girl has only trace amounts of HIV in her bloodstream and has been able to keep the virus that causes AIDS in check without the help of medication, doctors said Sunday at a medical conference in Atlanta.

If researchers demonstrate that the same treatment can work in other children, it could drastically alter the lives of the estimated 1,000 babies born with HIV every day, most of them in Africa, doctors said.

"If there is a trial that shows this can happen again, then this will be very important," said Dr. Karin Nielsen, a pediatrician who specializes in infectious diseases at UCLA's David Geffen School of Medicine who was not involved in the girl's case. "You'll be able to treat people very intensively and reverse the disease."

Attempting to replicate the results in other HIV-positive infants is "our next step," said Dr. Deborah Persaud, a virologist at Johns Hopkins Children's Center who described the Mississippi patient at the Conference on Retroviruses and Opportunistic Infections. She and others are to make a formal presentation during the conference's scientific program Monday.

Details of the unusual case have not yet been published in a medical journal so that other doctors and researchers can assess it. It's possible that the girl — although at high risk for contracting the virus from her mother — was not actually infected herself, skeptics said.

Researchers who have examined her case extensively say they believe she did have the virus but was able to knock it back before it had time to establish itself in parts of the immune system where it can remain dormant and strike again after drug treatments are stopped. Such viral reservoirs are essentially impossible to treat once they have been established.

"Is it possible the child was not infected? Yes. Is it likely? No," said Dr. Anthony Fauci, head of the National Institute for Allergies and Infectious Diseases. The virus probably could not have remained in the baby's body as long as it had if she had not been infected, he said.

In the United States and other developed countries, more than 98% of babies born to mothers with HIV do not get the virus thanks to preventive treatments that begin before birth and last up to six weeks afterward. In this case, the girl's mother did not know she had HIV until she took a screening test after she was already in labor, said Dr. Hannah Gay, the pediatric HIV specialist at the University of Mississippi Medical Center in Jackson who treated the baby.

Instead of giving the newborn just one antiretroviral drug, Gay opted for a three-drug regimen that is sometimes given as a long-term treatment for infected babies, she said. The first infusion was begun when the girl was only 30 hours old — several days before blood tests confirmed she was HIV-positive at birth, Gay said.

With continued treatment, it took less than a month for the girl's viral load to become undetectable with standard clinical tests, Gay said.

The treatments continued normally for about 15 months, then became sporadic. When the girl was 18 months old, her mother stopped bringing her to the doctor and she didn't receive her medications.

Five months later, the girl returned to the clinic and had her blood drawn. Gay said she expected to find that her viral load was high. Instead, her HIV levels were still undetectable. Additional tests a few days later confirmed the results, Gay said.

That's when Persaud and Dr. Katherine Luzuriaga, an immunologist at the University of Massachusetts Medical School, began studying the girl's blood. Using the most sensitive tests available, they were able to find tiny amounts of HIV "particles" but no virus capable of replicating, the research team reported.

The analysis was funded by the National Institutes of Health and amfAR, the Foundation for AIDS Research.

Among adults with HIV, a lucky few — less than 1 in 200 — are able to keep the virus at bay without the help of medications. But this girl is not one of these "elite controllers," Fauci said, because in her case doctors could not detect the presence of any virus capable of replication at all.

"You can always isolate virus from elite controllers," he said. "It's just that they control it so well, it doesn't replicate."

The case of the Mississippi patient is unusual because doctors would not stop a patient's treatment intentionally to see how he or she would fare without antiretroviral drugs. It is also unusual, Fauci said, because most pregnant women in the U.S. who are HIV-positive receive prenatal treatment to fight the virus, which dramatically decreases the risk of transferring the infection to the baby.